With serious health concerns over in-person voting at polling stations amid the coronavirus pandemic, more Americans will send their ballots in by mail this year than in any election in the nation’s history.

But the massive surge in voting by mail doesn’t come without controversy.

For months, President Trump has blasted attempts to increase mail-in balloting, repeatedly warning of “voter fraud” and a “rigged election.” Democrats have pushed back at what they call the president’s “baseless” charges and argue that Trump and the GOP are trying to suppress the vote.

COULD TRUMP'S ATTACKS ON MAIL-IN VOTING BACKFIRE?

Election experts do say that voting by mail is more susceptible to fraud than casting a ballot in person, but they’ve seen no evidence of widespread fraud or that absentee balloting favors Democrats. But the massive increase in absentee balloting places an extra burden on already stressed-out state and county election officials and on a U.S. Postal Service facing financial and manpower deficits.

Here's a look at which states vote entirely by mail and which states allow absentee balloting without an excuse.

Universal voting by mail

Five states already voted entirely by mail even before the pandemic. Twenty years ago, Oregon became the first state to go to universal mail-in balloting. They’ve been joined by Washington, Colorado, Utah and Hawaii. These states send ballots to all registered voters.

Amid the coronavirus, many states with both Democratic and Republican governors have moved to make it easier for voters to send in ballots by mail. In June, Democratic Gov. Gavin Newsom of California signed into law a measure that requires his state to send every registered voter a ballot. New Jersey, Vermont and the District of Columbia are doing the same.

Nevada’s Democratic governor also signed into law a bill that sends ballots to all registered voters in this year’s general election. The Trump re-election campaign, the Republican National Committee and the state GOP immediately filed a suit against Nevada over the new law, claiming that the measure will undermine the election’s “integrity.”

Montana is allowing its counties to automatically send absentee ballots to all registered voters, as they did during their June primary. Even though Montana will conduct its election nearly entirely by mail, the state will still provide in-person voting at polling stations.

No-excuse absentee balloting

Thirty-four states now allow for people to vote by absentee ballot without having to provide an excuse. That number’s been on the rise this year due to the coronavirus. Among the states that don’t require an excuse to cast an absentee ballot are the key general election battlegrounds of Florida, North Carolina, Pennsylvania, Michigan, Wisconsin, Ohio, Arizona, Georgia, Minnesota, Iowa and New Hampshire.

Some states are making it easier than others for voters to obtain absentee ballots. A handful of states – including Michigan, Wisconsin and Ohio – are sending absentee ballot applications to all or most registered voters.

And some states offer a permanent absentee ballot list. Once a voter asks to be placed on the list, that voter will automatically receive an absentee ballot for all future elections.

Excuse needed

Voters in just eight states need an excuse to obtain an absentee ballot. Traditional excuses include illness or military deployments. For voters in these states, in-person voting at polling stations remains the main option for casting a ballot.